Thursday, February 10, 2011

Digging Deep: The Vargas Shaft

What is 120-feet deep, 41-feet in diameter and supported by 76 concrete secant piles? If you have been following us for awhile you know this is none other than the Vargas Shaft! For those that are new or just need a refresher here is a run down:

The Vargas Shaft is one of the three locations where tunneling will take place for the New Irvington Tunnel. The shaft is located immediately east of I-680 off of the Vargas Road exit. A road header will be lowered into the shaft where it will tunnel west towards the Irvington Portal. As soon as this tunnel section is complete, the road header will reverse direction and tunnel eastward from Vargas towards Alameda West Portal where it will meet another road header coming from the Alameda West Portal. The tunnel rendezvous is scheduled to take place sometime in 2013.

Excavation of the shaft began in late January and is scheduled for completion by early March. The road header will be most of the way to the Irvington Portal by year's end.

Here's a progress photo of the Vargas Shaft. A yellow railing has been installed for safety. In the background, you can see the steel I-beams that are used for sound barriers.
















We will post more pictures as the project moves forward. Feel free to send any photos or videos you have of the project to fzamora@sfwater.org.

2 comments:

  1. why does it produce so much smoke every day?

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  2. Thank you for your comment!

    What you see actually isn’t smoke. It is mostly water mist with left-over dust particles in it that are being ventilated from inside the tunnel while it is being excavated. Here’s why:

    Digging a tunnel, particularly one that has to grind through hard rock, can produce a large amount of dust. The dust must be ventilated from inside the tunnel to create a safe breathing environment for the workers inside.

    To protect the general public on the outside, air from the tunnel ventilation system must be treated to remove dust particles. Air in the tunnel passes through a filter system, which uses water misters and special fabric panels to capture the dust particles. As result, what you see is the discharge from the tunnel ventilation system, which is composed of fine water particles and some residual dust particles.

    All the work that we do is in accordance with strict air quality and safety standards.

    If you have any other questions please feel free to contact Francis Zamora at fzamora@sfwater.org.

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